1. Technical Field of the Invention
The present invention relates to ion optic devices, and more particularly to manufacturing ion optic devices and components of ion optic devices which are dimensionally stable throughout variations in temperature.
2. Description of Related Art
Scientific instruments such as mass spectrometers, residual gas analyzers, mass filters, ion containment apparatus and particle beam accelerators all use ion optic components to manipulate ion particles. The accuracy of these scientific instruments is dependent, at least in part, on the dimensional precision of the ion optics therein.
For example, a mass filter such as a quadrupole, hexapole or octopole is used to separate ionized particles based on their mass-to-charge ratios. FIG. 1 depicts a generic quadrupole mass filter 100 that includes four parallel metal elongated electrodes 110, separated by ceramic interstitial supports 120. Two opposing electrodes 110 have an applied potential of negative polarity and the other two electrodes 110 have an applied potential of positive polarity. The applied voltages affect the trajectory of ions traveling down the xe2x80x9cflight pathxe2x80x9d centered between the four electrodes. For given voltages, only ions of a certain mass-to-charge ratio pass through the quadrupole filter and all other ions are thrown out of their original path. A mass spectrum is obtained by monitoring the ions passing through the quadrupole filter as the voltages on the electrodes are varied.
The performance of the mass filter is critically dependent on the mechanical accuracy of the individual poles (electrodes) and their relationship to each other. With variations in temperature, the electrodes and interstitial supports change dimensionally and the relative position of the electrodes varies. This affects the accuracy of the mass filter, for example, by varying the intensity of the electrical field in the flight path, which is undesirable. Other ion optic devices, such as an ion mirror, a pulser, an Einsel lense, and others, are also similarly affected by temperature.
In prior art devices, attempts have been made to construct ion optic devices that are dimensionally stable across a given temperature range by fabricating one or more components of these devices from materials having a low thermal expansion coefficient (hereinafter a xe2x80x9cthermally stable materialxe2x80x9d). However, it is difficult to find materials that are both thermally stable and that have other properties necessary for particular components required in an ion optic device. For example, in the quadrupole mass filter example above, the interstitial supports 120 are generally constructed from thermally stable ceramic materials. The electrodes 110 are commonly constructed of metal. Metals generally have a high thermal expansion coefficient, but are necessary in a mass filter because of their conductivity. Thus, some materials are chosen because they are thermally stable and some are chosen because they perform the function required of the component they embody. Ultimately thermal stability of the ion optic device is compromised.
Therefore, there is a need for a method which allows construction of ion optic devices and components thereof which are more dimensionally stable across temperature variations.
The exemplary embodiments of the present invention encompass a method of fabricating an ion optic device or components thereof which are substantially dimensionally stable over a given range of temperature. The method may include shaping a ceramic material into at least a portion of the ion optic device. At least a portion of the shaped ceramic material is then covered with at least one covering material. A portion of the covering material can be removed. The at least one covering material can be a conductive or a resistive material, such as a metal or semiconductor material. The ceramic material can be a ceramic, a glass, or a glass-ceramic.
A substantially cylindrical bore can be provided in the ceramic material. At least two portions of the covering material on opposing surfaces of the interior of the bore can be removed to create at least two separate, opposing areas of covering material.
A cavity can be provided in the ceramic material. At least one portion of the covering material circumscribing the interior perimeter of the cavity can be removed to create at least two substantially parallel bands of conductivity within the cavity. The cavity can extend through the ceramic material or can have a blind end. A conductive grid can be attached over one end of the cavity. The ceramic material can be separated into a first portion and a second portion and re-joined with a conductive grid therebetween. If the cavity is provided with a blind end, at least a portion of the blind end in the interior of the cavity is covered with the at least one covering material.
The exemplary embodiments of the present invention also encompass a device for manipulating ions in a vacuum. The device includes a ceramic substrate having a cavity therein. A conductive coating is provided on at least a portion of an interior surface of the cavity. The conductive receives an applied voltage to act upon the ions.